CSIS CSIS 4381

3-Input AND from Transistors

• Illustrates basic use of IDL-800• Illustrates construction of gates• Illustrates the “transistor bleed-through”

problem that affects the AND circuit.

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Transistors in Series

A

B

Out

C

V+

• Construction of 3-Input (A,B,C) AND from transistors.

• Note the resistor and output are at the “bottom”.

• Three inputs (from switches)

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Connection to Power

Next slide shows the connection to power.

+ 5 volt power supply.

Connects to top transistor A

B

Out

C

V+

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Connection to Ground

A

B

Out

C

V+After output.

Through the current-limiting resistor.

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Connection to Logic Switches

A

B

Out

C

V+Switches connect to each transitor.

Switches are either:

0-off, no voltage,

or 1-On, +5 volts

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Measuring Output with the Meter

A

B

Out

C

V+

2.13

• Digital Volt Meter connects to output, and to the ground.

• It measures the voltage differential between those two points.

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Measuring Output with a LED

The output can be connected to a Light Emitting Diode (LED) rather than to the DVM.

A voltage of around 2.5 and greater will cause the LED to light.

The LED is already wired on one end to the ground.

A current limiting resistor ensure that the LED does not receive too great a voltage and current.

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Voltage – 1 input on

A

B

Out

C

V+

2.13

Illustrates the “transistor bleed-through” effect.

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Voltage – 2 inputs on

A

B

Out

C

V+

2.84

Illustrates the “transistor bleed-through” effect.

Two transistors, larger voltage detected.

This voltage is large enough to be detected as a “1” by the LED.

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Voltage 3 inputs on

A

B

Out

C

V+

4.07

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“Bleed-Through” voltage can light an LED, and be detected as a “1”

A

B

Out

C

V+

2.83

Illustrates the “transistor bleed-through” effect.

Two transistors, larger voltage detected.

This voltage is large enough to be detected as a “1” by the LED.

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Use NANDs or NORs

• Need to support AND, OR and NOT as Boolean operations

• Manufacturing cost:– Single silicon layering

• don’t need to support two places (layers) to connect resistors, or measure output

• AND/OR different layer from NOT– Complete set of operations – NAND or NOR can

be wired for any logic• Fabricate a chip with one type of gate

• Avoids AND “transistor bleed-through” problem• Actual modern logic implementations will vary as

technologies evolve